The present invention relates to an electronic component such as a proximity sensor as well as a method of manufacturing the same, and in particular to a structure of an electronic component provided with a casing filled with resin as well as a method of manufacturing such an electronic component.
FIG. 35 is a cross section showing an example of a proximity sensor of a high-frequency oscillation type in the prior art. A conventional proximity sensor 101 includes a core 102 provided with an annular groove, in which a coil 104 held by a coil spool 103 is buried. Core 102 is held at a front surface of a coil casing 105 made of resin as shown in the figure, and these parts are accommodated in a base member, i.e., metal casing 106. A reference number 107 indicates an electronic circuit which includes an oscillator circuit including coil 104 as well as a signal processor unit for detecting lowering of its oscillation amplitude, and is mounted on a printed board 108. After coil 104 is connected to printed board 108, primary filler resin 109 is supplied into a portion of coil casing 105 near core 102 for stabilizing performance. In order to improve environmental resistance, epoxy resin 110 is supplied into the casing of the proximity sensor. When supplying epoxy resin 110, it is hot and, for example, an injector is used. A clamp portion 111 holds a code 112 to complete the proximity sensor. Alternatively, there has been a proximity sensor, in which a casing is not filled with resin in a sealed manner, and thermoplastic resin is used to form an integral structure. A display element 113 is mounted on printed board 108, and light beams emitted therefrom are led externally through a transparent light conducting portion 114.
For filling the casing of the proximity sensor with the resin, primary filler resin 109 of a low viscosity is injected into the coil casing 105, and coil 104 held by core 102 is inserted into the resin. Then, metal casing 106 is fitted to the coil casing 105, and epoxy resin 110 is injected again. In this conventional manner of filling the structure with resin, many steps are required for resin injection, and a long time is required for hardening.
The conventional proximity sensor requires a preliminary process such as stirring of resin to be injected. Even if the filler resin is injected into the casing with an injector or the like, it shrinks when hardened, so that additional resin must be injected to fill the space formed by shrinkage. Therefore, many steps are required, and a long hardening time of about 1 hour is required. Further, in the case where thermoplastic resin is used for forming an integral structure, a high injection pressure is required for molding, so that accommodated parts may be impaired.
In the case where resin of a high viscosity is used as the filler resin for forming an integral structure, spaces around the coil casing, coil spool, core and others are not completely filled with the primary filler resin, and air remains in the primary molding dies. The remaining air expands due to a high temperature of the dies and a high temperature of the filler resin during the primary molding, and the coil casing may be deformed. The air remaining around the coil may cause unstable characteristics of the coil.
The present invention has been developed for overcoming the above disadvantages through low-pressure molding with thermoplastic resin, and has the following objects.
An object of the invention is to enable easy and reliable filling of a casing of an electronic component with resin. Another object of the invention is to simplify a resin filling process.
The invention provides an electronic component having a casing accommodating an electronic part and filled with resin, and including a resin inlet arranged at one end portion of the casing, and a passage arranged at the other end portion of the casing for communicating an interior and an exterior of the casing with each other. Since the passage for air is arranged remote from the resin inlet, air in the casing can be discharged through the passage to lower the pressure in the casing during supply of the resin. Therefore, resin can be easily and reliably supplied to portions, for example, around the electronic part in the casing, which cannot generally be filled with resin without difficulty. Further, the resin can be hardened in a short time, so that processing steps can be reduced in number, and a manufacturing time can be significantly reduced.
The passage arranged at the other end side of the casing may be arranged at a cover or lid covering an opening formed at the other end side of the casing. The passage formed at the other end side of the casing may be arranged between a cover over an opening formed at the other end portion of the casing and the casing. The resin inlet may be arranged at a clamp portion attached to an opening formed at the one end portion of the casing for holding a code. In a structure wherein a coil casing is arranged in the casing, the air passage may be formed of an air discharge groove arranged between a cylindrical casing and a coil casing. In a structure wherein a printed board and a shield film covering the printed board are arranged in a cylindrical casing, an opening may be formed at the shield film. The air passage may be formed by forming a linear projection at the coil casing.
The present invention also provides a method of manufacturing an electronic component wherein an electronic part is accommodated in a casing filled with resin and having a resin inlet at its one end portion and a passage at the other end portion for communicating an interior of the casing with an exterior of the same, the method including the steps of lowering a pressure in the casing by externally discharging air in the casing through the passage, and filling the casing with resin by supplying the resin. In this manner, the pressure in the casing is reduced for supply of the resin. Therefore, it is possible to supply reliably and easily the resin to a portion which cannot be generally filled with the resin without difficulty. In this case, the resin is hardened in a short time, so that the processing steps can be small in number, and the manufacturing time can be significantly reduced.